An initial inquiry into power failures on the West Coast railway line has said the faults were not caused by its new faster timetable, the BBC has learned.
Network Rail sources said each of a recent catalogue of incidents had a different cause, none of which were related to modernisation work.
BBC transport correspondent Tom Symonds said Network Rail had been accused of rushing the work.
But a briefing note on the causes of the faults said that was not the case.
Passengers on the line between London and Scotland have suffered delays and cancellations in the past week due to a string of problems, from power failures to cracked rails, and a plane crash on the track.
Our correspondent added that the note said the failure of overhead lines near Wembley on Tuesday could be been blamed on an insulator rod which was incorrectly installed two years ago, and came apart.
Problems at Bletchley, Buckinghamshire, on Monday were the result of a snapped cable, and an incident at Watford Junction the day before was caused by a loose wire which got caught up in the overhead line mechanism.
Both these faults were described as rare.
Network Rail dismissed suggestions it has a persistent problem on the line, but said its investigations continued.
Cracked rail
Last year the line underwent £9bn of improvements.
A new timetable brought in on 14 December by Virgin Trains hailed improved services and shorter journey times. But a blown fuse in north-west London on day one brought slight delays.
On 2 January, a light aircraft crashed into power lines over a stretch of the line near Little Haywood in Staffordshire, killing three people. The line between Rubgy and Stafford was closed over the weekend.
By Sunday, Network Rail engineers were fixing the damaged track and power lines, and services were almost back to normal by Monday morning rush hour.
But damaged overhead power cables at Watford Junction meant Sunday trains in and out of Euston were cancelled.
Network Rail engineers worked overnight to fix the lines in time for Monday.
Day seven
However by Tuesday two more overhead cable were damaged, one north of Rugby in the West Midlands, the other at Bletchley in Buckinghamshire.
On Tuesday night overhead power cables hit a train at Kenton in north-west London, closing the line between North Wembley and Kings Langley, Hertfordshire, until Wednesday.
A cracked rail between Coventry and Birmingham then caused more delays.
A fallen power cable in north-west London resulted in all London Midland and Virgin services trains in and out of London's Euston station being halted on Wednesday.
On Thursday travellers experienced delays for the seventh day in a row because of overhead power line problems in the Midlands.
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